The combination of a chiller and an evaporative cooler is often used to remove heat from a building, equipment, etc. In general, a chiller provides cooled water for cooling a building, equipment, etc., and an evaporative cooler provides water to the chiller for cooling heated return water. A first recirculation loop carries chilled water from the chiller to the building, equipment, etc., where the chilled water is used to extract the heat. After extracting the heat, the water is then recirculated back to the chiller. Heat is then removed from the recirculated water by the evaporative cooler. To this end, a second recirculation loop delivers cool water from the evaporative cooler to the chiller. The chiller transfers the heat from the recirculated water to the cool water from the evaporative cooler. The second recirculation loop then returns the now heated, evaporative cooler loop water to the evaporative cooler. The evaporative cooler removes the heat from the evaporative cooler loop water, thereby generating a continual supply of the cool water that is supplied to the chiller.
In addition to transferring heat by increasing the temperature of outside air, the evaporative cooler also increases the relative humidity of the air thereby transferring heat via the heat of vaporization. Therefore, the amount of heat that can be transferred by the evaporative cooler is dependent on both the temperature and the humidity of the outside air. Accordingly, for some outside conditions where the evaporative cooler cannot run as efficiently due to humidity, when the evaporative cooler is controlled to supply cool water to the chiller at a set temperature, the evaporative cooler will be driven at maximum capacity and the water that the evaporative cooler supplies to the chiller will exceed the set temperature.